This invention relates to hydronic heating systems for dwellings, offices, etc. having heating loops that consist of tubing or pipes held in the floor or walls of a room by radiation panels that contain a metal radiation plate that radiates heat to heat the room, the tubing being secured in the panels in intimate thermal contact with the metal radiation plate; and, more particularly, where the metal plate is in two parts that attach to the edges of side-by-side boards and provide the radiation plate and a metal slot into which the tubing is inserted and held in thermal contact with the plate.